1. Field of the Invention
The present invention relates generally to the field of suspension devices. More particularly, the present invention relates to control systems and methods that utilize a specially tuned damper, controller, and sensor to trigger an end stop function.
2. Description of the Related Art
In vehicle use, vibrations, shock, and motion resulting from uneven road surfaces are transferred to a vehicle operator through the operator's seat. Over time, these conditions may lead to dangerous vehicle operation, fatigue, lower-back pain, osteoarthritis and leg discomfort. Typically, seats used in commercial and public transportation vehicles, such as trucks and buses, include suspension systems that aid in reducing the discomfort felt by the vehicle operator. These suspension systems typically include a mechanical device, such as a damper, attached between two structural members, such as a seat frame and a vehicle chassis. Dampers are well known which use a fluid as the working medium to create damping forces/torques and to control vibration, motion and shock. In particular, controllable dampers are well known that include electrorheological fluid (ER), electrophoretic fluid (EP), magnetorheological fluid (MR), hydraulic fluid, etc. In simple suspension systems passive dampers may be used. In more complicated suspension systems, adjustable dampers and controllers may be used to control the movement of the damper components and prevent end stop collisions.
Under certain conditions, some or all of these conventional suspension systems provide little transition into the end stops, and the end stops themselves tend to be very abrupt and uncomfortable for the operator. The end stops are defined as the maximum mechanical limits of system travel. Generally, there are shock reducing snubbers, often elastomeric, that are designed into the system. However, if the system velocity is high enough when an end stop collision occurs, a very rapid impact may result. This bottoming or topping imparts unwanted stresses to the mechanical components in the system (e.g. linkages, swing arms, bushings, joints, etc.), is detrimental to the system's overall life, can be an annoyance to the seat occupant, and may effect the physical health of the seat occupant. More significantly, when a vehicle operator experiences an end stop collision, the motion in the seat may lead to a loss of control of the vehicle.
Various methods have been employed to control vibration in seat suspension systems. Generally, in such prior art control methods, operating conditions are obtained by at least one sensor which supplies system operating information to a processor that determines the appropriate primary control signal to be sent to an electro-mechanical device, such as a magnetorheological (MR) fluid damper, for controlling vibration. A number of the various prior art methods for controlling vibration are described in the following issued United States patents: “Skyhook Control” as described in U.S. Pat. No. 3,807,678 to Kamopp et al.; “Relative Control” as described in U.S. Pat. No. 4,821,849 to Miller; “Observer Control” as described in U.S. Pat. No. 4,881,172 to Miller; “Continuously Variable Control” as described in U.S. Pat. No. 4,887,699 to Ivers et al.; “Delayed Switching Control” as described in U.S. Pat. No. 4,936,425 to Boone et al.; “Displacement Control” as described in U.S. Pat. No. 5,276,623 to Wolfe; “Rate Control” as described in U.S. Pat. No. 5,652,704 to Catanzarite; “Modified Rate Control” as described in U.S. Pat. No. 5,712,783 to “Method for AutoCalibration of a Controllable Damper Suspension System as described in U.S. Pat. No. 5,964,455 to Catanzarite; and “End Stop Control Method” as described in U.S. Pat. No. 6,049,746 to Southward et al.
One conventionally controlled ride management system uses a passive damper to reduce seat motion. Soft passive dampers provide smooth mid-ride performance but leave the seat occupant vulnerable to the uncomfortable and possibly harmful effects of topping and bottoming during unexpected large vibration inputs. Firm passive dampers, on the other hand, may minimize topping and bottoming, but mid-ride performance is compromised. Another version of a passive damper is used where the driver may manually adjust between a soft ride and a firm ride. This still has the same disadvantages discussed above.
A simple controllable damper technique for suspension control involves using a controlled bleed arrangement to shape the force velocity curve in the low-speed region, and adjusts the control signal to the damper to control the desired level of control. One damper is used for each corner of the car, for example. However, there is no form of end stop control.
A more advanced seat suspension control system used to maintain comfortable driving conditions by reducing vibration, shock, and motion is the Motion Master® Ride Management System offered for sale by the Lord Corporation (Lord Corporation, Cary, N.C.). The Motion Master® system is made up of four components. The first is a position sensor operable for monitoring movement of the seat caused by changing road and operating conditions. The second is a controller that continuously receives signals from the position sensor, determines optimal damping forces and is capable of adjusting at a rate of 180 times per second. The third is a shock absorber (damper) operable for responding to the controller within milliseconds. The last component is a ride mode switch that enables the vehicle operator to choose among different ride options, such as soft, medium and firm settings based on the operator's preference. The position sensor and shock absorber are separate units that are mounted between two structural bodies. The shock absorber contains a magnetically responsive fluid that when subjected to a magnetic field is capable of changing from a near-solid to a liquid and back in a matter of milliseconds. The stronger the magnetic field, the more viscous the fluid and the greater the damping force.
What is needed is a simple and inherently low-cost damping control method for any type of suspension system, such as a suspended seat. What is needed is a damper and control method that can be used where the cost of a full featured damper controller cannot be tolerated, and where the performance benefits of controllable damping are of value. Other non-seating applications, such as an automobile suspension for example, may also benefit from such a low-cost high-function damping system.